Molarity Calculator Online Free Tool
Molarity Calculator
Calculator Inputs
Molarity Formula
M = m / (MW × V)
Molarity = Mass / (Molecular Weight × Volume)
Calculation Results
0.0000 g
0.0000 mg
0.0000 g/mol
Molar mass of compound
0.0000 L
0.0000 mL
0.0000 M
0.0000 M
Solution Details
0.000000 mol
0.0000 M
0.0000 mM
0.0000 μM
0.0000 g/L
0.0000 mg/L
0.0000 kg/m³
0.0000 mol/m³
0.0000 g/L
Interactive Visualizations
Shows how concentration changes with serial dilutions of your solution
Understanding Concentration Units
Molar Concentration Units
M (Molar)
Moles of solute per liter of solution
mM, μM, nM
Millimolar, micromolar, nanomolar (10⁻³, 10⁻⁶, 10⁻⁹ M)
mol/m³
SI unit: 1 M = 1000 mol/m³
Mass Concentration Units
g/L, mg/L, kg/L
Mass of solute per volume of solution
ppm (parts per million)
Equivalent to mg/L for dilute aqueous solutions
ppb (parts per billion)
Equivalent to μg/L (1000× more dilute than ppm)
kg/m³, g/m³
SI units: kg/m³ = g/L, g/m³ = mg/L
Note: Mass concentration units (g/L, ppm, etc.) require molecular weight for conversion to molarity. The calculator automatically handles these conversions based on your selected units.
Common Laboratory Solutions
Physiological Saline
0.9% NaCl
0.154 M
154 mM
Blood Glucose
~90 mg/dL
0.005 M
5 mM
Lab HCl Solution
Standard acid
1 M
1000 mM
Concentrated HCl
37% solution
12 M
12000 mM
Dilute NaOH
Weak base
0.1 M
100 mM
Molarity (M) is the concentration of a solution expressed as moles of solute per liter of solution. It is the most common unit of concentration in chemistry, and is fundamental to preparing laboratory reagents, performing stoichiometric calculations, and understanding physiological concentrations. This calculator converts between mass, moles, volume, and molarity, and solves dilution problems using the C₁V₁ = C₂V₂ formula.
Molarity Formulas
The key to molarity calculations is converting mass to moles first using the molecular weight (molar mass). Once you have moles, divide by the volume in liters to get molarity. For dilutions, the number of moles is conserved — only the volume changes, which reduces the concentration proportionally.
Molarity (M) = Moles of Solute / Liters of Solution Moles = Mass (g) / Molecular Weight (g/mol) Combined: M = (Mass in g) / (MW × Volume in L) Dilution: C₁V₁ = C₂V₂ (Concentration₁ × Volume₁ = Concentration₂ × Volume₂)
Example: 5.85g NaCl (MW=58.44) in 500 mL water. Moles = 5.85/58.44 = 0.1 mol Molarity = 0.1 mol / 0.5 L = 0.2 M
Common Laboratory Solutions
Standard concentrations are used across labs to ensure reproducibility. Many solutions are prepared as concentrated stock solutions and then diluted to working concentrations. Knowing the stock concentration and applying C₁V₁ = C₂V₂ is the standard approach.
| Solution | Common Concentration | Typical Use |
|---|---|---|
| Normal saline (NaCl) | 0.154 M = 0.9% w/v | IV fluids, cell biology buffers |
| HCl (concentrated) | ~12 M | Acid cleaning, pH adjustment (dilute before use) |
| NaOH (1M standard) | 40 g/L | Titrations, pH adjustment |
| Phosphate buffer (PBS, pH 7.4) | 10-50 mM | Cell culture, immunoassays |
| Glucose (IV solution) | 5% w/v ≈ 0.278 M | IV dextrose solutions |
| Ethanol (70%) | ~12 M | Disinfection, precipitation |
| Acetic acid (concentrated) | ~17.4 M | Glacial acetic acid — dilute carefully |
Serial Dilutions
Serial dilutions are repeated dilutions used to prepare a range of concentrations spanning many orders of magnitude. They are common in microbiology (counting colonies), biochemistry (standard curves), and pharmacology (dose-response assays). Each step dilutes the previous step by the same factor.
Each step: C_new = C_previous × (V_transfer / V_total) For 1:10 serial dilution (take 1 mL, add to 9 mL): ×0.1 each step Starting at 1 M: → 0.1 M → 0.01 M → 1 mM → 0.1 mM → 0.01 mM Total dilution after n steps = (dilution factor)^n After 6 steps of 1:10: 10⁻⁶ = 1 millionth of original concentration
Use the same size transfer volume each step for consistent dilution factor. Rinse the pipette tip between transfers to avoid carry-over errors.
Concentration Units Reference
Molarity is the most common but not the only concentration unit. Understanding the relationships between them is essential when working across different fields or converting between literature values.
| Unit | Definition | When Used |
|---|---|---|
| Molarity (M) | mol solute / L solution | Most chemistry applications |
| Molality (m) | mol solute / kg solvent | Colligative properties (boiling/freezing point) |
| Normality (N) | Equivalents / L | Acid-base and redox titrations |
| % (w/v) | g solute / 100 mL solution | Biology, pharmacy, food science |
| % (v/v) | mL solute / 100 mL solution | Alcohol and liquid-liquid mixtures |
| ppm (mg/L) | mg solute / L solution | Trace analytes, water quality |
| μM / nM / mM | Micro/nano/millimolar | Biology, pharmacology (very low concentrations) |
Frequently Asked Questions
What is the difference between molarity and molality?⌄
Molarity (M) = moles per liter of solution — the solution volume includes both solvent and solute. Molality (m) = moles per kilogram of solvent only. For dilute aqueous solutions, they are approximately equal. For concentrated solutions, they diverge because adding solute changes the total volume (affecting molarity) but not the mass of the solvent (molality unchanged). Molality is temperature-independent and preferred for calculations involving boiling/freezing point changes (colligative properties), because volume changes with temperature but mass does not.
How do I make a 1M NaCl solution?⌄
Calculate the mass needed: 1 mol of NaCl = 58.44 g (molar mass). Weigh out 58.44 g of NaCl on an analytical balance. Dissolve in about 800 mL of distilled water with stirring — NaCl dissolves readily. Transfer to a 1 L volumetric flask. Add distilled water to bring the total volume to exactly 1 L (use the calibration mark). The solution is 1.000 M NaCl. Safety note: always add solute to solvent, not the reverse — this is critical for concentrated acids and bases that can release significant heat.
How do dilutions work?⌄
C₁V₁ = C₂V₂ (concentration × volume is conserved). To make 100 mL of 0.1 M HCl from a 1 M stock: V₁ = (C₂ × V₂) / C₁ = (0.1 × 0.1L) / 1 = 0.01 L = 10 mL. Take 10 mL of 1 M HCl and add water to bring the total volume to 100 mL. This is a 1:10 dilution (1 part concentrate to 9 parts water). For accurate dilutions, always measure into a volumetric flask and add diluent to the mark, not the other way around.
What is the difference between percent concentration and molarity?⌄
Percent concentration (w/v) = grams of solute per 100 mL of solution. Molarity accounts for molecular weight and expresses concentration in moles. 5% glucose = 5 g/100 mL = 50 g/L. Molecular weight of glucose = 180.16 g/mol. Molarity = 50 / 180.16 = 0.278 M. Percent concentration is more intuitive for simple preparations and is common in biology and pharmacy. Molarity is essential for stoichiometric calculations (reaction amounts, titrations, dosing by moles) because chemical reactions occur based on molar ratios, not mass ratios.
What is normality and when is it used instead of molarity?⌄
Normality (N) = equivalents of solute per liter, where an "equivalent" is the reactive amount per mole. For acids, one equivalent = one mole of H⁺ it provides. 1 M H₂SO₄ is 2 N (it provides 2 H⁺ per molecule). For bases, one equivalent = one mole of OH⁻. Normality simplifies titration calculations because N₁V₁ = N₂V₂ at the equivalence point regardless of the acid/base valence. Modern chemistry has largely replaced normality with molarity (specifying the exact reaction), but normality still appears in older literature and some clinical and industrial settings.